I have a suggestion. Pull the thermostat out. Put it on the stove in a pot of water and slowly heat it up. Keep checking the water temp while observing when the tstat opens. Be sure to stir the water while doing this. My bet is yours is like most replacement stats, and it opens too hot. I've had many common replacement 180 tstats, that are new, open at close to 200F. My recommendation is to buy a robertshaw style tstat from a v8 muscle era mopar application. I have had no issues with robertshaw stats opening at the correct temp. After learning this many years ago, I check all new stats this way before installing. Hope this helps.